Abstract

Bridging nanometer to macroscopic length scales is a major challenge to nanoscience. Low symmetry building blocks and assemblies offer possibilities for complex “smart” material behavior by introducing anisotropy and sometimes endowing macroscopic objects with nanoscale quantum properties. Field-driven synthesis and assembly is a promising strategy for the fabrication of responsive hierarchical structures. This talk will focus on several examples of such research. First, we describe a novel mechanism for electrostatic cooperative self-assembly of dense nanoparticle monolayers on surfaces. Second, we use electric and magnetic fields for manipulating magnetic Janus particles and characterize the forces between them. The Janus particles can be assembled in different low symmetry configurations and even disassembled on demand. Third, we present novel types of foams stabilized by composite magnetic particles and investigate their breakdown on demand. The foams exhibit extraordinary stability in the absence of fields, but can be destroyed instantaneously by the application of a threshold magnetic field. We also discuss the use of mechanical shear fields as an alternative to electric and magnetic fields for the fabrication of nanofibers. 1D structures, such as nanofibers, can exhibit quantum- scale confinement and molecular alignment effects, yet allow easy, macroscopic handling at the same time. We have recently developed a process for massively parallel fabrication of nanofibers from polymer solution droplets, based on shear fields in an antisolvent precipitation medium. We have investigated the fundamental processes involved in the fiber formation as well as the opportunities for scalable nanofiber manufacturing by this method. The methods presented would have applications in numerous areas, including fabrication of nanostructured substrates, photovoltaic energy production, smart, responsive liquid, gel, and solid materials, and novel tissue engineering scaffolds.